Common lambsquarters response to glufosinate as

Common Lambsquarters Response to Glufosinate as Influenced by Humidity
Carl Coburn* and Andrew Kniss, University of Wyoming, Laramie.
INTRODUCTION
•
•
•
•
•
•
The efficacy of many POST herbicides is influenced by species and environmental conditions
before, during, and after application (Muzick 1976)
Air temperature and relative humidity (RH) are known to alter herbicide activity (Anderson et
al. 1993)
High RH promotes uptake and translocation of foliar applied herbicides
Wild-oat (Avena fatua) showed reduced response to glufosinate in a low RH environment
(Ramsey et al. 2006)
Glufosinate has limited use in the semi-arid regions of the western U.S. because of variable
efficacy on key weed species
Glufosinate may be a useful tool to help manage herbicide resistance in the West if efficacy
can be improved
RESULTS AND DISCUSSION
•
There was a significant interaction between glufosinate rate and RH but no effect of adjuvant
• The labeled application rate of 451 g ai ha-1 provided nearly 100% control of common
lambsquarters in the HH treatment 14 and 21 DAT
• The highest doses of glufosinate in the HH and LH treatments resulted in greater than 90%
control
• Common lambsquarters control in the HL and LL treatments never reached 80% at 14 DAT
• These results suggest that RH after the time of treatment may be more important for
glufosinate efficacy on common lambsquarters compared to RH before treatment
Figure 2. Common lambsquarters control 14 and 21 DAT
MATERIALS AND METHODS
• Common lambsquarters seeds were planted in 164-ml plastic cones filled with 1:1 mixture of
sand and potting mix
• Cones were sub-irrigated and placed in one of two growth chambers (Percival Model E-36LI)
kept at 22 C with a 16-hour day length
• Growth chambers were kept at 38% or 86% average RH
• A three-factor factorial design with three replicates was used:
• Four RH treatments were established by growing plants in either high (H) or low (L)
humidity, then replacing the plants after treatment into either the same (HH, LL) or
different (HL, LH) growth chambers such that all combinations of low and high
humidity before and after application were obtained (HH, HL, LH, LL)
• Glufosinate was applied at 200, 400, 800, 1200, 1600, and 2000 g ai ha-1 plus
ammonium sulfate
• For each glufosinate rate, three adjuvant treatments were used: no adjuvant,
nonionic surfactant at 0.25% v/v or methylated seed oil at 1% v/v
• Common lambsquarters control was assessed visually 14 and 21 days after treatment (DAT)
• A three-parameter log-logistic model was used to analyze the effect of RH on glufosinate
efficacy (Seefeldt et al. 1995)
Y = f(x) = D/ (1 + (x/ED50)B)
where
x= rate of glufosinate, D= upper limit, B= slope at inflection
point of the curve, and ED50= dose giving 50%
response
Table 1. Glufosinate ED50 and B-parameter estimate at 14 DAT
RH before/after treatment
Glufosinate ED50 ± std. err.
B parameter ± std. err.
High/High (HH)
139 ± 60.9
-4.2 ± 5.1
High/Low (HL)
688 ± 314
-1.1 ± 0.3
Low/High (LH)
414 ± 24.7
-2.3 ± 0.3
Low/Low (LL)
828 ± 453
-1.1 ± 0.3
Figure 1. Glufosinate at 2000 g ai ha-1 on plants in low RH before and after treatment
LITERATURE CITED
Anderson, D.M., C.J. Swanton, J.C. Hall, and B.G. Mersey. 1993. The influence of temperature and
relative humidity on the efficacy of glufsoniate-ammonium. Weed Rsrch. 33: 139-147.
Muzik, T.J. 1976. Influence of environmental factors on toxicity to plants. Herb. Phys. Biochem.
and Ecol. 1: 203-247.
Ramsey, R.J.L., G.R. Stephenson, and J.C. Hall. 2006. Effect of humectants on the uptake and
efficacy of glufosinate in wild oat (Avena fatua) plants and isolated cuticles under dry
conditions. Weed Sci. 54: 205-211.
Seefeldt, S.S., J.E. Jensen, and E.P. Feurst. 1995. Log-logistic analysis of herbicide dose-response
relationships. Weed Tech. 9: 218-227
Scan here to download a PDF version of this poster: